Highly functional thermoplastic resins whose use and variety are expected to further increase in the future, with the widespread use of durable consumer goods, are required to be finely collected in accordance with their resistance and moldability and supplied for recycling as thermoplastic resins of higher quality. The use of highly functional thermoplastic resins is increasing, particularly in household appliances and automobiles. In particular, when talking about the highly functional thermoplastic resins used in optical components and high-strength members, the manufacturing processes are complicated and the raw materials are expensive; therefore, it is preferable that highly functional thermoplastic resins can be recycled at a quality level closer to that of the original products.
Typically employed current methods of collecting thermoplastic resins by specific gravity and/or charging characteristics, although they may be simple, are not suitable for finely collecting highly functional thermoplastic resins. For example, because the heat resistance and moldability required for many highly functional thermoplastic resins differ depending on their usage (television sets, automobiles, etc.), various adjustments are made for each usage, including changing the molecular weight, mixing polymers having different molecular weights, copolymerizing various monomers, and adding functional groups, and in some cases, different polymers are mixed and polymer alloys are formed. Through such adjustments, thermoplastic resins having a great variety of characteristics can be formed from a limited number of organic compounds (monomers) as required. These adjustments, however, do not result in mutual differences in specific gravity and charging characteristics among highly functional thermoplastic resins; thus, it is difficult to collect them by their specific gravity and/or charging characteristics.
In addition, when an adjustment is carried out based on molecular weight, collecting becomes impossible even if spectral analysis, such as infrared analysis, is conducted. For copolymers, mixtures of polymers, and polymer alloys, identification by spectral analysis is possible to a certain extent, but it is virtually impossible to accurately identify and collect large amounts of the various thermoplastic resins contained in different percentages in a thermoplastic resin mixture.
To carry out recycling at a quality level closer to that of the original products, it is necessary to collect the thermoplastic resins more finely. Specifically, the thermoplastic resins must be collected based not only on their material name (e.g., ABS, cycloolefin, polyimide, etc.) but also on their molecular weight and properties, e.g., heat resistance or moldability. Heat resistance is determined by the use of the material, and moldability is determined by the requirement of the product. Low moldability causes defects in the product and greatly affects product quality.
With the thermoplastic resin, heat resistance is directly affected by the softening point, which is represented by Tg (glass-transition point), and moldability is affected by the storage elastic modulus in the temperature range from the glass-transition point to the melting point (rubber elasticity range). Such properties are generally referred to as rheological characteristics (dynamic viscoelasticity) as a whole. Some thermoplastic resins have similar backbones and thus have substantially the same Tg but exhibit different properties in their rubber elasticity range (e.g., different storage elastic modulus, etc.). Since such thermoplastic resins are mainly adjusted to improve their moldability, it is preferable to separate such thermoplastic resins and to reuse recycled thermoplastic resins produced from such thermoplastic resins in products similar to the products the thermoplastic resins were originally used in.